This invention is in the field of positive displacement pumps.
It is known that the delivery pressure of a rotary pump, especially a gear pump, can be adjusted by modifying the gap losses between the lateral flank or flanks of one or more of the gear wheels and the housing in which these wheels are enclosed. This modification of the gap can be accomplished where one or more of the gear wheels and the wall of the housing opposite thereof can be displaced with respect to one another, the displaceable or mobile wall of the housing can respond to the pressure in the pump and be opposed by a resilient means. When a certain delivery pressure in the pump is exceeded, a gap occurs between the gear wheel or the gear wheels and the movable side of the housing, through which gap liquid can flow back from the pressure side to the suction side of the gear wheel or the gear wheels.